1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing the same and, more particularly, to a semiconductor device that has an excellent barrier capability in its miniaturized contact section and a method for manufacturing the same.
2. Description of Related Art
With higher device miniaturization, higher density integration, and increased multiple layers of LSI devices, it has become an important object to develop techniques for embedding wiring material in miniaturized through holes with greater aspect ratios. In the conventional technique, a tungsten plug is embedded in a through hole in a contact section, for example, in order to plug the through hole and to prevent reaction between aluminum of the wiring layer and silicon of the silicon substrate. The through hole typically has an aperture diameter of 0.5 xcexcm or smaller and an aspect ratio of 2 or greater. However, such a contact structure tends to result in greater electrical resistance of the tungsten, deterioration of resistance to electromigration, and lowered production yield due to its complicated forming process. Many attempts are being made to develop techniques for embedding aluminum in through holes without requiring a complicated embedding process that is currently required for tungsten plugs.
However, contact sections that use aluminum require thorough countermeasures against junction leaks that may be caused by reaction between the aluminum and silicon of the silicon substrate, and also require a high barrier capability of a barrier layer.
For example, a barrier layer is formed from a nitride layer of a high melting point metal, such as a titanium nitride layer, that is formed in a nitrogen atmosphere by reaction sputtering. Such a barrier layer has the following problems. {circle around (1)} A titanium nitride layer, when formed by reactive sputtering in a nitrogen atmosphere, has an insufficient coverage. Therefore, it does not provide a sufficient coverage at a bottom portion of a miniaturized through hole having a high aspect ratio. {circle around (2)} A titanium nitride layer, when formed by reactive sputtering in a nitrogen atmosphere, has large film stresses and therefore tends to develop microscopic cracks. As a result, aluminum in the wiring material tends to diffuse and cause junction leaks. {circle around (3)} A titanium nitride layer, when formed by reactive sputtering in a nitrogen atmosphere, has columnar crystals. As a result, aluminum tends to diffuse through crystal grain boundaries, causing junction leaks. {circle around (4)} The crystal orientation of a titanium nitride layer determines a  less than 111 greater than  crystal orientation of an aluminum layer. Because the crystal orientation of a titanium nitride is not always uniform, the plane azimuth in the  less than 111 greater than  crystal orientation of the aluminum layer differs. As a result, the surface of the aluminum layer roughens, and alignment becomes difficult in photolithography of the aluminum layer. {circle around (5)} Further, a titanium nitride layer, when formed by reactive sputtering in a nitrogen atmosphere, occasionally peels off during film formation because of its own film stresses and therefore tends to generate particles. The particles pollute the surface of the wafer and cause short-circuits, and therefore are a source of lowered production yield.
It is an object of the present invention to provide a semiconductor device having a miniaturized contact section of a half-micron or less in size that enables optimum embedding of a conductive material in the miniaturized contact section, and that achieves a high barrier capability without causing junction leaks. The present invention also relates to a method for manufacturing the semiconductor device.
In accordance with one embodiment of the present invention, a semiconductor device includes a semiconductor substrate having a device element and an interlayer dielectric layer formed on the semiconductor substrate. A through hole is formed in the interlayer dielectric layer. A barrier layer is formed on surfaces of the interlayer dielectric layer and the through hole. A wiring layer is formed on the barrier layer. In accordance with one embodiment of the present invention, the barrier layer includes at least a metal oxide layer and a metal nitride layer. The metal oxide layer is composed of an oxide of a metal that forms the barrier layer. The metal nitride layer is composed of a nitride of the metal that forms the barrier layer. As a result, the barrier layer presents a high conductivity and an excellent barrier capability.
In one embodiment, the barrier layer may preferably include a first metal oxide layer, a metal nitride layer, and a second metal oxide layer. The first metal oxide layer is composed of an oxide of a metal that forms the barrier layer. The metal nitride layer is composed of a nitride of the metal that forms the barrier layer. The second metal oxide layer is composed of an oxide of the metal that forms the barrier layer. In one embodiment, the first and second metal oxide layers that form the barrier layer may preferably be in an amorphous form. As a result, the barrier layer attains a high barrier capability.
The first metal oxide layer that forms the barrier layer may preferably have a film thickness of about 5-30 nm in consideration of its barrier capability and conductivity. In a similar manner, the second metal oxide layer that forms the barrier layer may preferably have a film thickness of about 5-30 nm. These metal oxide layers may be continuous or discontinuous to one another.
The wiring layer may preferably be formed from aluminum or an alloy to containing aluminum as a main component. In addition to aluminum and an aluminum alloy, other materials, such as, for example, copper, gold, white gold and the like, may also be used for the wiring layer. Depending on the requirements, tungsten plugs may also be used as a material for embedding through holes.
A semiconductor device in accordance with one embodiment of the present invention is manufactured by a method including the steps of forming a through hole in an interlayer dielectric layer formed on a semiconductor substrate having a device element, and forming a barrier layer on surfaces of the interlayer dielectric layer and the through hole, and forming a wiring layer on the barrier layer. In one embodiment, the barrier layer may be formed by the following process: (a) a metal layer that forms the barrier layer is formed on a semiconductor substrate; (b) a heat treatment is conducted in a hydrogen atmosphere to form a hydrogenated alloy of the metal layer or cause occlusion of hydrogen in the metal layer; (c) the metal layer is contacted with oxygen in an atmosphere including oxygen; and (d) a heat treatment is conducted in a nitrogen atmosphere to form a metal oxide layer and a metal nitride layer.
In the above-described manufacturing method, the barrier layer may include a metal oxide layer and a metal nitride layer. In one embodiment of the present invention, the barrier layer includes a first metal oxide layer composed of an oxide of a metal that forms the barrier layer, a metal nitride layer composed of a nitride of the metal that forms the barrier layer, and a second metal oxide layer composed of an oxide of the metal that forms the barrier layer.
In the manufacturing method in accordance with one embodiment of the present invention, a single metal layer may be formed by a sputtering method or a CVD method in step (a). Then, a metal nitride layer is formed in step (d). As a result, the barrier layer is formed with better cohesiveness and coverage at bottom sections of through holes compared to, for example, a metal nitride layer that is directly formed by a sputtering method. Also, after the metal layer is formed in step (a), the metal layer is processed in step (b) to form a hydrogenated alloy of the metal layer or to cause occlusion of hydrogen in the metal layer. As a consequence, reaction between silicon of the semiconductor substrate and a metal of the metal layer is suppressed in a heat treatment that is later performed. As a result, nitrogenization reaction and oxidation reaction of the metal are securely performed in step (d), with the result that the metal nitride layer and metal oxide layer are formed. As a result, the barrier capability of the barrier layer is greatly improved, and the conductivity of the barrier layer is secured because of the presence of the metal oxide layer.
It is not very clear why the metal oxide layer is formed in two layers, namely, a first metal oxide layer and a second metal oxide layer, with a metal nitride layer being formed in between. It is believed that such a structure is formed in the following manner. Oxygen is occluded in the metal layer that is formed in step (a). When the metal layer is brought in contact with oxygen in step (c), the oxygen is introduced in the inside of the metal layer and/or adsorbed on the surface of the metal layer. Then, in the heat treatment in step (b), a part of the first metal oxide layer is formed, and in the heat treatment in step (d), formation of the first metal oxide layer further progresses and the metal nitride layer and the second metal oxide layer are formed.
In step (b), the heat treatment may preferably be conducted at temperatures of about 200-800xc2x0 C. to sufficiently form a hydrogenated alloy of the metal layer or sufficiently cause occlusion of hydrogen in the metal layer. The hydrogen content of the hydrogen atmosphere may preferably be at about 1-100%, depending on the treatment temperature.
In step (c), the atmosphere including oxygen may preferably include at least 10% oxygen and, more preferably, about 10-30% oxygen. In this step, oxygen is brought in contact with the surface of the metal layer that has changed to a hydrogenated alloy or is occluded with hydrogen in step (b).
In step (d), the heat treatment may preferably be conducted at temperatures of about 600-900xc2x0 C., so that separation of hydrogen as well as nitrogenization and oxidation of the metal layer take place. The pressure of the atmosphere in step (d) is not limited to a particular range, but may preferably be at normal pressure.
The metal that forms the barrier layer may preferably include, in view of good barrier capability and the conductivity, at least one selected from a group consisting of titanium, cobalt, ruthenium, molybdenum, hafnium, niobium, vanadium, tantalum and tungsten.
The metal layer that forms the barrier layer may preferably have a film thickness of about 50-150 nm in consideration of the film thickness of the metal nitride layer and the metal oxide layer formed in a step later performed.
Other features and advantages of the invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, various features of embodiments of the invention.